Fluoroscopic tables are commonly used for supporting a patient in a position to be irradiated by a beam of X-rays or other selected radiation. One conventional type of X-ray apparatus for diagnostic purposes includes a table having a top upon which the patient is positioned during the diagnostic procedure, and an X-ray source which is located above the patient and which directs X-rays downwardly through the patient and table top to a bucky which is carried by the table beneath the patient. The bucky includes an X-ray film cassette or carrier that positions the plane of the film substantially parallel to the table top. Such prior art apparatus is disclosed in U.S. Pat. No. 3,967,126 issued on June 29, 1976 to George W. Otto, Jr.
Later developments in the field of X-ray fluoroscopy included the production of X-ray image intensifiers which replace the bucky when it is desired to obtain immediate fluoroscopic viewing of an irradiated area. The image intensifier is an electron imaging device which converts an X-ray image first to an electron image and then to a visible image. Thus, when an X-ray beam is directed through a patient, there is formed an X-ray image which is directed onto the face of the image intensifier which immediately forms a visible image which may be viewed by the doctor or technician without waiting for development of films. Filming or television reproduction of the visible images produced by the image intensifier are also possible by known techniques.
One type of prior art system utilizing an X-ray image intensifier is disclosed in U.S. Pat. No. 3,912,936, issued Oct. 14, 1975 to Cunninghame et al.
Image intensifiers and their associated optical or reproducing apparatus make up a fluoroscopic staging which is extremely bulky and the combined weights of the staging components may approach as much as 450 to 500 pounds, for example. When such fluoroscopic staging is used, the X-ray generator is placed beneath the table top and the staging is located above the patient. The staging and X-ray generator must always be aligned and, therefore, they are located at opposite ends of a tower which extends vertically from the back of the table and is movable in a direction longitudinally or parallel to the table top.
Since great physical effort is required when scanning a patient during a fluoroscopic examination, a motor drive is conventionally used for powering the system to simultaneously move the staging and generator so as to position the apparatus in desired position with respect to the area of the patient's body to be irradiated. Numerous power drives or assists have been designed to minimize the effort required by a fluoroscopist. It has been found advisible to keep the manual effort for this purpose to between two and six pounds, for example, in any direction of scanning. However, the problem becomes even more complicated when the system components must be moved vertically such as when the table is in an upright position. Also, it is very important to the fluoroscopist that he maintain complete control of all motions of the apparatus and that the power assist not overdrive.
A conventional motor drive system employing constant voltage or constant power drive will produce wide variations in assist effort depending on load velocity and variations in load due to high friction spots, slight misalignments, etc. This negates the feeling of complete control by the operator.